Due to the limited bandwidth resources, the Long Term Evolution (LTE) standard provides the LAA technology and the LSA technology to integrate bandwidth resources of different heterogeneous network architectures.
When a wireless network system adopts the LAA technology, an available Primary Component Carrier (PCC) is a band licensed by the LTE, while available Secondary Component Carriers (SCCs) are other bands (e.g., Wi-Fi bands) not licensed by the LTE. When the wireless network system adopts the LSA technology, the available PCC is also a band licensed by the LTE, while the available SCCs are other licensed bands (e.g., bands for military use, or TV white bands).
Adopting either the LAA technology or the LSA technology, a base station has to access resources of bandwidth of the SCCs via the LTE technology. According to the conventional technology, if the SCC is a Wi-Fi band, the base station has to perform listen-before-talk (LBT) on the Wi-Fi band and perform Clear Channel Assessment (CCA). If the base station ensures that a band is idle during the process of performing CCA, the base station transmits a reservation signal on the band to reserve the resource of the band. In this way, the base station itself and/or a user equipment (UE) can transmit data on the band.
There are two kinds of conventional technologies for performing CCA. The first kind of technology is called the Frame Based Equipment (FBE). The FBE adopts fixed-length frames. That is, a CCA time interval of a fixed length is defined in the frame. The base station/equipment probes the SCC in this fixed CCA time interval. If an interference value probed by the base station on the SCC is smaller than a threshold, the base station can use the SCC. If the base station misses the CCA time interval, the base station has to wait until next CCA time interval, which results in an increased data transmission delay. Another kind of technology is called the Load Based Equipment (LBE), wherein the CCA time interval in the frame architecture used in the LBE is extendable. As this technology is based on the load, the number of CCA time intervals that a base station needs to probe is different. Specifically, the number of CCA time intervals in which the base station needs to probe increases as the load of the base station increases.
No matter which of the conventional technologies is used, it is the base station that performs the CCA and then notifies the UE of the band that is to be used. When several base stations instruct UEs (transmitting terminals) to use a same band to transmit data to other UEs (receiving terminals) within the same overlapped coverage, the so called Hidden Terminal problem will occur.
Accordingly, there is an urgent need for a channel selection technology that will not increase the delay time and will not cause the hidden terminal problem.